Photovoltaic devices such as solar cells are capable of converting solar radiation into usable electrical energy. The energy conversion occurs as a result of what is well-known in the solar cell field as the photovoltaic effect. The magnitude of the photovoltage and photocurrent from a single solar cell is insufficient for practical applications such as powering electrical motors, communications, and the like. Therefore, a plurality of solar cells are normally interconnected in what is known as a solar array to provide sufficient voltage and current for useful applications. The solar cells are connected in series in a solar array when a higher voltage is needed or in parallel when a higher current is needed. Depending upon the use, solar cells may be both connected in parallel and in series in a single solar cell array.
The solar cells can be interconnected by soldering an interconnect layer of a suitable metal, such as copper or silver, between adjacent solar cells. However, solder interconnects are subject to thermal degradation and generally exhibit low peel strengths at high temperatures which render them unsuitable in solar arrays which operate at above about 185.degree. C. temperatures, such as solar concentrators or in applications which require high peel strengths such as military space applications or terrestrial applications where the solar cell array is anticipated to be subjected to a high degree of abuse.
A welded interconnect can withstand high temperatures and abuse; however, general welding techniques can crack the microstructure of the solar cell, and can cause the migration of metal from the metalization layers to the solar cell structure, which results in a general degradation of the electrical output of each individual solar cell in the solar array. Electrical degradation due, inter alia, to microcracking and diffusion of metals from the metalization layers during the welding operation is defined as the percentage decrease in the peak power output of an illuminated solar cell. The degradation is thought to be caused by localized junction damage caused by the welding process.
Thus, it would be highly desirable to have a method of interconnecting solar cells which does not crack the microstructure of the solar cell, or degrade the performance of the solar array, and, in addition, can withstand high temperatures and provide an interconnect with high peel strength to withstand harsh space and rugged terrestrial applications.